Journalists show a picture of Edward Snowden, to passengers arriving in Moscow from Aeroflot flight SU213. Photograph: Igor Kharitonov/EPA

Edward Snowden was five hours into his flight from Hong Kong, having already been served one of two hot meals, when news of his departure to Moscow began to electrify media organisations all over the world.

The Hong Kong authorities waited until Snowden was safely out of Chinese airspace before sending out a short press release that confirmed the intelligence whistle-blower had been allowed to leave on Aeroflot flight SU213, bound for Russia.

The 30-year-old had not been stopped on his way to Chek Lap Kok airport, and was allowed to slip away on a hot and humid morning, despite American demands that he be arrested and extradited to face trial for espionage offences.

The reason?

The Americans had mucked up the legal paperwork, the authorities claimed in a statement released at 4.05pm local time.

Hong Kong had no choice but to let the 30-year-old leave for "a third country through a lawful and normal channel".

If the sudden "discovery" of a flaw in legal proceedings prompted sighs of relief around the island and across the rest of China, there would have been sharp intakes of breath in Washington and London, where diplomats and intelligence officials had been hoping the net around Snowden was finally tightening.

A fortnight into a series of revelations that have embarrassed and infuriated the National Security Agency and Britain's GCHQ, their target was on the move again, heading, it seems, to central or south America, and potentially beyond the reach of authorities that could try to shut him up.

The escape from Hong Kong was another audacious move from Snowden, who went to ground a week ago and has not been seen since.

It was choreographed with the help of WikiLeaks, whose legal director is Baltasar Garzón, the former Spanish judge who enraged the British government by issuing an international warrant for the arrest in the UK of former Chilean president General Augusto Pinochet. "The WikiLeaks legal team and I are interested in preserving Mr Snowden's rights and protecting him as a person," Garzón said.

Once on board the Airbus A330-300, and for perhaps the first time in two weeks, Snowden would have been unaware of the diplomatic rows raging 40,000ft below him, as American officials woke up to find that the former NSA contractor had eluded them again and China reacted with indignation to his latest revelations.

The White House appears to have been caught flat-footed by the latest manoeuvres. On Saturday, President Obama's national security adviser, Tom Donilon, told CBS news he expected Hong Kong to arrest Snowden because it "has been a historically good partner of the United States in law enforcement matters and we expect them to comply with the treaty in this case".

Lawyers in Hong Kong thought so too, and reacted with amazement to the statement from the Hong Kong Special Autonomous Region (HKSAR).

Simon Young, a public law specialist at the University of Hong Kong, said the decision was "a shocker".

"The US government will be irate with their Hong Kong counterparts [and] may even question whether the Hong Kong government was acting in good faith pursuant to their treaty obligations. I'm surprised."

Ronny Tong Ka-wah, a barrister and legislator for the pro-democracy Civic party, said letting Snowden leave with a minimum of fuss must have been China's preferred option.

"If Beijing was to refuse to surrender Snowden, that might harm Sino-US relations. On the other hand, if Beijing was to allow Snowden to surrender, it might well be subject to criticism both here in Hong Kong and in European countries making noises about the conduct of the US."

The formal response from the US department of justice was measured.

"We will continue to discuss this matter with Hong Kong and pursue relevant law enforcement co-operation with other countries where Mr Snowden may be attempting to travel," a statement said.

But on Capitol Hill there was undisguised fury, particularly when it emerged that Snowden appeared to be intending to leave Moscow for Cuba, and then possibly Venezuela or Ecuador.

"Every one of those nations is hostile to the United States," fumed Mike Rogers, chair of the House intelligence committee. "The US government must exhaust all legal options to get him back. When you think about what he says he wants and what his actions are, it defies logic."

Democrat senator Charles Schumer said Russia's president, Vladimir Putin, "always seems almost eager to stick a finger in the eye of the United States, whether it is Syria, Iran and now, of course, with Snowden".

General Keith Alexander, director of the NSA, was withering too. "[Snowden] is clearly an individual who's betrayed the trust and confidence we had in him. This is an individual who is not acting, in my opinion, with noble intent."

The row overshadowed further revelations about the scope of US spying activities. Snowden left Hong Kong reeling after disclosing to the South China Morning Post that the NSA had targeted Chinese phone companies in a mass trawl of texts and phone calls.

After years of being condemned by Washington for industrial-scale stealing and spying in cyberspace, Beijing seized the opportunity to hit back, while swerving around awkward questions about Snowden himself.

The official Xinhua news agency said the revelations had "put Washington in a really awkward situation. Washington should come clean about its record first. The United States, which has long been trying to play innocent as a victim of cyber attacks, has turned out to be the biggest villain in our age."

In Moscow, meanwhile, various welcoming parties gathered at Terminal F of Sheremetyevo international airport in anticipation of Snowden's arrival. The biggest comprised reporters from the world's media, who assembled airside to greet the US fugitive and his travelling companion, Sarah Harrison, who works for WikiLeaks.

Neither of them emerged into the public lounges, provoking a new round of conspiracy theories and rumours about where they might have gone.

Russian security vehicles surrounded the plane when it landed, while plain-clothed Russian agents trawled the terminal, deflecting questions about which state agency they represented by pretending to be businessmen from Munich and journalists from state-run NTV.

Then a Venezuelan contingent was said to be there, fuelling speculation that Snowden was being whisked away to the country's embassy in Moscow, and his final destination was Caracas.

But by early evening it appeared Snowden had not left the airport at all, and Quito was a more likely final destination. The Ecuadorian foreign minister, Ricardo Patiño, on an official visit to Vietnam, tweeted that Snowden had sought political asylum in his country.

An Aeroflot source quoted by Interfax said Snowden had taken a small overnight "capsule" room at a hotel in terminal E.

"He has arrived. He cannot leave the terminal, since he doesn't have a Russian visa," the source was quoted as saying.

The appearance at the airport of Ecuador's ambassador, Patricio Chávez, added to the melee.

The envoy appeared lost as he wandered around the terminal, approaching a group of journalists to ask: "Do you know where he is? Is he coming here?" A reporter replied: "We thought you did."

Before wandering off, Chávez admitted he hoped to see Snowden because "we have an interest in knowing what is happening to him". And, perhaps, how he had got there in the first place.

As Snowden settled in for the night, the American authorities announced they had revoked his passport before he had got on the flight from Hong Kong, and they hoped Moscow might intervene on their behalf.

But Russian officials have given no indication that they have any interest in detaining Snowden or have any grounds to do so. Far from it. The foreign minister, Sergey Lavrov, has said Russia would be willing to consider granting asylum if Snowden were to make such a request.